This invention relates to a process for converting gaseous lower alkanes, e.g. methane, to synthesis gas by partial oxidation.
In view of the dwindling supplies worldwide of liquid petroleum, there is a growing interest in natural gas as an industrial feedstock. Natural gas is primarily composed of methane and there is a great interest in efficient processes for converting this methane into synthesis gas. Synthesis gas, a mixture of carbon monoxide and molecular hydrogen is a valuable industrial feedstock for the manufacture of a wide variety of useful chemicals.
A common commercial source of synthesis gas has been the steam reforming of coal or natural gas. However, it is an inefficient and very energy intensive process for this purpose.
Catalytic partial oxidation is a much more energy efficient process and a number of such industrial processes have been developed. One process is described in Kobylinski U.S. Pat. No. 5,112,527, issued May 12, 1992. This process used as partial oxidation catalyst the so-called xe2x80x9cplatinum groupxe2x80x9d metals of Group VIII of the periodic table, e.g. platinum or palladium supported on alumina. However, in that process, no more than 20% conversion from methane to synthesis gas could be carried out because of the formation of coke.
Bhattacharyya et al. U.S. Pat. No. 5,399,537, issued Mar. 21, 1995 describes a process for conversion of methane to synthesis gas by partial oxidation using a hydrotalcite-like compound, e.g. a compound of the formula NiMg5Al2(OH)16CO3.
In Green et al. U.S. Pat. No. 5,431,855, issued Jul. 11, 1995 a method is described for converting a gas mixture comprising CO2, O2 and CH4 into a product gas mixture comprising H2 and CO by a combined partial oxidation-dry reforming reaction. For this procedure there was used a solid catalyst of the formula MxMxe2x80x2yOz where M is Mg, B, Al, Ga, Si, Ti, Zr, Hf or Ln and Mxe2x80x2 is Fe, Os, Co, Rl, Ir, Pd, Pt, Ni or Ru.
Green et al. U.S. Pat. No. 5,149,464, issued Sep. 22, 1992 describes a process for partial oxidation of methane to synthesis gas again using a solid catalyst of the formula MxMxe2x80x2yOz where M is Mg, B, Al, Ga, Si, Ti, Zr, Hf or Ln and Mxe2x80x2 is Fe, Os, Co, Rl, Ir, Pd, Pt, Ni or Ru.
There has been a very strong recent interest in mesoporous zeolites as catalyst for a variety of chemical processes. A mesoporous catalyst of particular interest is the MCM-41 family. These catalysts are described in a number of patents including U.S. Pat. Nos. 5,198,684 and 5,270,273, incorporated herein by reference. The MCM-41 mesoporous catalysts are typically alumina silicates with pore diameters in the range of about 20-100 xc3x85. These catalysts have been found to be particularly useful for the oligomerization of olefins.
It is an object of the present invention to provide an improved process for the catalytic partial oxidation of methane to synthesis gas that maintains a high methane conversion with minimal carbon deposition.
The present invention in its broadest aspect relates to the catalytic partial oxidation of lower (C1-C4) alkanes to synthesis gas in which there is used as partial oxidation catalyst a mesoporous alumino silicate solid catalyst having the structure of MCM-41 and further having a nickel loading of about 5-20% by weight. The MCM-41 catalyst used in the present invention typically has a silica-alumina ratio of at least about 5:1 typically 5:1-1000-1, and pore diameters of about 15-100 xc3x85.
The nickel, in the form of NiO, may conveniently be deposited on the MCM-41 catalyst by an incipient wetness technique. The resulting catalyst is calcined in order to obtain the oxide form of the nickel. The calcined form of the catalyst is then loaded into the reactor and reduced in-situ.
Using the above catalyst, a high reactivity towards the conversion of methane is maintained as well as a high selectivity to carbon monoxide and hydrogen. For instance, methane conversions to synthesis gas of over 80% have been maintained with selectivities to CO and H2 of higher than 95%, while using reaction temperatures no higher than 750xc2x0 C.